A Study of Efficacy and Safety of FXS6837 in Anti-C5 Treated PNH Patients.

Inclusion criteria: 1. Male or female subjects aged ≥ 18 years at screening; 2. Body weight ≥ 40 kg and body mass index (BMI) ≥ 18 kg/m2 at screening; 3. Diagnosis of PNH at least 6 months before screening and confirmed by high-sensitivity flow cytometry with a PNH RBC and granulocyte/monocyte population size of ≥10% within 6 months before screening or during screening; 4. Have received a stable treatment regimen (dose and dosing interval) with anti-C5 monoclonal antibody (eculizumab) for at least 6 months prior to the first dose; 5. Have at least one blood transfusion record within 3 months before screening, or Hb level persistently \< 100 g/L during stable treatment with anti-C5 monoclonal antibody within 3 months before screening (medical history data/laboratory test reports, at least 2 test records with an interval of ≥ 4 weeks); 6. Hb meeting one of the following conditions: (1) Hb concentration \< 100 g/L at the first screening visit, and received RBC transfusion therapy due to PNH-related anemia during the screening period; (2) Mean Hb concentration from two measurements during the screening period \< 100 g/L and all Hb measurements \< 105 g/L during the screening period (these two measurements should be 2 to 6 weeks apart; multiple Hb measurements are allowed during the screening period); 7. Vaccinated against Neisseria meningitidis and Streptococcus pneumoniae before the first dose. If patients have not been previously vaccinated or need booster vaccination (according to local vaccination policies), vaccination should be completed at least 2 weeks before the first dose. If the first dose must occur within 2 weeks after vaccination, prophylactic antibiotic treatment should be used until at least 2 weeks after vaccination; 8. Participants of reproductive potential commit to having no plans for pregnancy or sperm/egg donation from screening until 1 month (female participants) or 3 months (male participants) after the last dose and voluntarily take effective physical contraceptive methods (including partners); 9. Have a detailed understanding of the nature, significance, possible benefits, potential inconveniences, and potential risks of the trial, and voluntarily participate in this clinical trial; Able to communicate well with the investigators and comply with the requirements of the entire study; Signed a written informed consent form. Exclusion criteria: 1. With laboratory evidence of bone marrow failure during screening (reticulocyte count \< 100 × 109/L, or platelet count \< 30 × 109/L, or neutrophil count \< 0.5 × 109/L); Received acute treatment (such as platelet transfusion, granulocyte colony-stimulating factor) for thrombocytopenia or neutropenia within 30 days before screening; 2. Participants receiving other therapies before screening that have not reached the following stable treatment durations: * Erythropoietin for at least 8 weeks * Immunosuppressants for at least 8 weeks, systemic corticosteroids (≤ 15 mg/day) for at least 4 weeks * Iron, vitamin B12, or folic acid supplementation for at least 4 weeks * Anticoagulants: Vitamin K antagonists (such as warfarin) used for at least 4 weeks with a stable international normalized ratio (INR) (as determined by the investigator), low molecular weight heparin, oral anticoagulants such as aspirin, rivaroxaban, apixaban, etc., for at least 4 weeks; * Hypoxia-inducible factor prolyl hydroxylase inhibitors (HIF-PHI) for at least 8 weeks; * Androgens for at least 4 weeks; 3. History of malignant tumors of any organ or system within 5 years before screening (except local basal cell carcinoma of the skin or carcinoma in situ of the cervix), regardless of whether treatment was received and whether there is evidence of local recurrence or metastasis; 4. History of bone marrow/hematopoietic stem cell or solid organ transplantation (such as heart, lung, kidney, liver); 5. History of splenectomy or planned surgery during the study period; 6. Subjects with significantly abnormal liver function at screening: any parameter of alanine aminotransferase (ALT), γ-glutamyl transpeptidase (GGT), or alkaline phosphatase (ALP) \> 3 × ULN; 7. Human immunodeficiency virus (HIV) infection (HIV antibody positive), active syphilis infection, hepatitis B virus infection (hepatitis B surface antigen positive), active hepatitis C virus infection, or active tuberculosis infection at screening; 8. Concurrent systemic critical diseases, including but not limited to: advanced heart disease (such as New York Heart Association \[NYHA\] Class IV), severe lung disease (such as severe pulmonary hypertension \[WHO class IV\]), active hepatitis, severe kidney disease (estimated glomerular filtration rate \[eGFR\] \< 30 mL/min/1.73 m2 or chronic kidney disease \[CKD\] stage 4 or dialysis patients), unstable thrombosis, active gastrointestinal hemorrhage, other blood disorders (such as chronic anemia unrelated to PNH), which are deemed unsuitable for study participation by the investigator; 9. Known or suspected by investigators to have immunodeficiency diseases or hereditary complement deficiency; 10. History of Neisseria meningitidis infection; History of ≥ 2 episodes of pneumococcal infection; 11. Detected or suspected (as assessed by the investigator) systemic active bacterial, viral (including COVID-19), or fungal infections within 2 weeks before the first dose; Axillary temperature \> 38 °C within 7 days before the first dose; 12. Suspected or known history of allergies to the IMPs or any ingredient in the IMPs; 13. Received any type of live attenuated vaccine within 4 weeks prior to screening, or plan to receive any live attenuated vaccine during the study; 14. Pregnant or lactating women or those with positive pregnancy test results; 15. Previous history of drug abuse or drug use; 16. Participated in other clinical trials of investigational drugs (or are still within 5 half-lives of the drug, whichever is longer) (except eculizumab) or medical device clinical trials within 30 days prior to screening, plans to participate in other clinical trials during the study, or having residual effects as assessed by the investigator; 17. Having diseases or medical conditions that affect drug absorption, distribution, metabolism, and excretion, or may reduce compliance or increase participant risk, such as severe gastrointestinal disease history, major gastrointestinal surgery history, swallowing difficulties, etc., as assessed by the investigator; Participants who may not be able to complete this study for other reasons, or other situations deemed unsuitable for study participation by the investigator.